Biliary atresia is the most common cause of neonatal cholestasis and if untreated results in end-stage liver disease (ESLD) and death. Even with current treatment strategies most children develop progressive liver disease and require liver transplantation for salvage. Biliary atresia is the number one indication for pediatric liver transplantation. Despite its importance, the pathogenesis of biliary atresia is unknown. One possible cause is an infection by an environmental agents such as viruses in a susceptible host. We established an experimental mouse model of biliary atresia and found that biliary injury in mice could be induced by a specific rotavirus species - rhesus rotavirus (RRV) in a susceptible murine host - BALB/c mice that progresses to ESLD and death. The inflammatory cholangiopathy is initiated at the biliary epithelial cell level and mirrors the disease process that is found in infants. This model will be used to define the molecular mechanisms regulating the interaction between a virus and the biliary system testing the over-arching hypothesis that the biliary atresia results from the abnormal recognition and infection of biliary epithelial cells (cholangiocytes) by a virus. This hypothesis will be addressed by the following specific aims: 1) Determine the specific RRV gene(s) necessary for the induction of biliary atresia in mice. 2) Determine the mechanism by which the cholangicoyte is susceptible to RRV infection. 3) Determine the mechanism by which RRV infected cholangiocytes triggers a host inflammatory response. The rotavirus property of gene reassortment will be used to identify the RRV gene(s) that cause the murine model of biliary atresia. A novel in vitro model in which RRV is able to infect a cholangiocyte cell line will be used to identify the mechanism by which RRV infects the cholangicoyte. Flow cytometry was used to detect the presence of the integrin apha2beta1 known to confer vulnerabiity to rotavirus infection. Blocking studies using natural ligands and monoclonal antibodies against this protein will be performed to determine its role. In vitro, cholangiocytes infected by RRV produce chemokines. This may be the triggering mechanism by which the host inflammatory response is initiated. We will determine if a similar process occurs in vivo. We will also determine if the NF-kappaB intracellular pathway is the mechansim by which RRV infection induces chemokine production.